event:list throws an exception if the Listeners directory does not exist

[sebdesign]

• Laravel Version: 5.8.9
• PHP Version: 7.2
• Database Driver & Version: N/A

Description:

When running php artisan event:list that was introduced in #28085 on an application that doesn't have an app/Listeners directory,
an InvalidArgumentException is thrown from the in method of the Symfony Finder, because it can't find that directory.

I believe this exception will also occur in the EventServiceProvider when shouldDiscoverEvents returns true, because the DiscoverEvents class will be invoked.

Steps To Reproduce:

laravel new blog
cd blog
php artisan event:list

[driesvints]

Ping @themsaid

[themsaid]

opened a PR to exclude non-existing directories:

#28098